Surface acoustic wave resonator, surface acoustic wave resonator unit, surface mounting type surface acoustic wave resonator unit

ABSTRACT

A surface acoustic wave resonator unit using surface acoustic wave, in which a surface acoustic wave resonator formed by disposing an IDT and reflectors on a piezoelectric member thereof is mounted by a cantilever method so that a surface acoustic wave resonator unit exhibiting very stable resonance frequency, a low resonance resistance and a large Q-value is realized. By accommodating the surface acoustic wave resonator in a housing in a vacuum state, the Q-value can be enlarged. By anodic-oxidizing the electrodes forming the IDT, a thick oxide film can be formed, the oxide film enabling the electrodes to be protected from problems, such as short circuit taking due to foreign matters, such as dust, with the characteristics maintained. If the high performance surface acoustic wave resonator unit is molded together with a lead frame by resin, a surface acoustic wave device, that can be mounted on the surface, and that exhibits excellent reliability and high quality, can be provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface acoustic wave resonator unitsuitable to form a high-frequency oscillation circuit and an apparatusthat exhibit excellent stability.

2. Description of Related Art

A technique for machining small articles, such as integrated circuits,causes fine electrodes to be formed on the surface of a piezoelectricmember, thus enabling surface acoustic waves (SAW) to be electricallydriven or detected. By using this technique, high frequency waves fromabout 100 MHz to the GHz level have been stably obtained. A surfaceacoustic wave device using the surface acoustic waves has been used toform a high-frequency filter (a surface acoustic wave filter) or asurface acoustic wave resonator unit (a SAW resonator unit) for formingan oscillation circuit.

FIG. 27 shows a known surface acoustic wave device. The device 90 has asurface acoustic wave resonator 92 that is, by an adhesive agent 93,secured to a supporting metal portion 91 and sealed in a case 96, byresistance welding or the like, performed in a nitrogen atmosphere.Leads 94 for establishing the electrical connection with the surfaceacoustic wave resonator 92, penetrate an insulating portion in the metalportion 91, which is a sealing glass 97. The leads 94 are electricallyconnected to electrodes disposed on the surface acoustic wave device bybonding wires 95.

The known surface acoustic wave device 90 shown in FIG. 28 is aso-called entire-surface adhesive type surface acoustic wave device thathas: a base 101 made of ceramic or the like; and a surface acoustic waveresonator 92 attached to the base 101 by an adhesive agent 93. The base101 has electrodes metallized thereon for establishing the electricalconnection with the surface acoustic wave resonator 92 so that theelectrodes on the base 101 and the electrodes on the surface acousticwave resonator 92 are electrically connected to one another by bondingwires 95 similarly to the foregoing structure. Furthermore, a cap 102is, by an adhesive agent or the like, attached above the base 101 in anatmosphere of nitrogen. The cap 102 is sometimes attached by brazing,welding or the like.

FIG. 29 shows a surface acoustic wave resonator 110 to be accommodatedin the foregoing surface acoustic wave device. The surface acoustic waveresonator 110 is formed by using a piezoelectric member 111, such as aquartz crystal member. The piezoelectric member 111 is obtained bycutting a flat piezoelectric substrate to a predetermined size anddimension, the piezoelectric member 111 being usually formed into arectangular shape as later described by cutting because an area fordisposing a reflector can be obtained, a satisfactory mass productivitycan be realized, and machining can easily be performed. An interdigitaltransducer (IDT) 112 is formed in a substantially central portion ofeither side (the main surface) of the piezoelectric member 111 by usinga thin film electrodes made of aluminum material or the like.Furthermore, reflectors 113, each of which is made of a thin film ofaluminum material or the like similar to the electrodes, are disposed onthe two sides of the IDT 112 in the lengthwise direction of the same,that is, on the two sides of the longer sides of the piezoelectricmember 111. Along the lengthwise directional edges of the piezoelectricmember 111, connection lands 114 are connected to the IDT 112 forconducting electric power are formed by using the same material as thatof the IDT 112. Therefore, the electrical connection can be establishedby performing wire-bonding to the connection lands 114.

To form a high-frequency-range and stable oscillator by using thesurface acoustic wave device, a surface acoustic wave device having alarge Q-value (sharpness of resonance) and a low resonance resistanceand, therefore capable of resonating a stable resonance frequency, isrequired. A conventional surface acoustic wave device of the foregoingtype comprises a surface acoustic wave resonator brought into closecontact with a support substrate by an adhesive agent. Therefore, thedifference in the coefficient of thermal expansion between the surfaceacoustic wave resonator and a portion for supporting the same,contraction of the adhesive agent, deformation of the supporting portionand the like cause the surface acoustic wave resonator to be distorted,as a result of which the resonance frequency to be made instable or theresonance resistance, is increased. Since many of these surface acousticwave devices have been used as surface acoustic wave filters,considerably large Q-values have not been required. However, a surfaceacoustic wave resonator that forms an oscillator must be capable ofgenerating resonance frequencies more stably than that required for thefilter. Therefore, it is important to use a surface acoustic waveresonator unit having a low resonance resistance and a large Q-value inorder to realize a stable oscillator.

In order to obtain a reliable oscillator, the device for forming thesame must have excellent reliability. In a surface acoustic wave device,adhesion of foreign matter, such as dust, to the surface, on which theIDT has been formed, causes a problem to arise in that the frequency ischanged or stable resonance characteristics cannot be obtained. If theconnection between the IDT and the lead becomes defective, stableoscillation characteristics cannot, of course, be obtained, and anincrease in the connection resistance occurring due to the defectiveconnection causes the frequency to be changed and the Q-value to belowered. Accordingly, it is also important to provide a reliable deviceby eliminating influence of foreign matter and preventing a defectivestate of connection while preventing influence of distortion on thesurface of the surface acoustic wave resonator.

SUMMARY OF THE INVENTION

In the present invention, influence of a supporting member or anadhesive agent on a surface acoustic wave resonator is prevented bysupporting only an end of the surface acoustic wave resonator. That is,only either end of a surface acoustic wave resonator in the lengthwisedirection of the surface acoustic wave resonator having an interdigitaltransducer formed in a substantially central portion of the surfacethereof, that is cut into a substantially rectangular shape, isconnected to the supporting member so that portions, which are affectedby the supporting member, are decreased. Furthermore, the surfaceacoustic wave resonator floats from a housing, such as a case. As aresult, the surface acoustic wave resonator is free from external stressand influence, due to distortion, can be eliminated so that a surfaceacoustic wave resonator unit having a very stable resonance frequencyand exhibiting excellent aging characteristics is obtained. That is,mounting of a portion more adjacent to the end than the reflectors(hereinafter called "mounting by a cantilever method") enables influenceof distortion upon the surface acoustic wave resonator to be eliminatedsatisfactorily.

As the structure of the housing for mounting the surface acoustic waveresonator by the cantilever method to form a surface acoustic waveresonator unit, a metal case formed into a cylindrical shape; a roundcan shape; or a box-like shape and sealed by a supporting member may beemployed. The "cylindrical shape" includes a structure having a circularcross sectional shape and that having an oval cross sectional shape. Ifa cylindrical case is used, the surface acoustic wave resonator ismounted substantially in parallel to a direction in which the case isattached. If a round can or box-like case is used, it is mountedsubstantially perpendicular to the direction in which the case isattached. The electrical conduction with the surface acoustic waveresonator, thus sealed in the housing, can be maintained by a pluralityof leads of the supporting member. The box-like ceramic case may be usedto perform sealing. In this case, a deducing pattern may be used tomaintain the electrical connection.

The present invention results in a fact to be found that a Q-value ofthe surface acoustic wave resonator unit, which is a device usingsurface acoustic wave of a piezoelectric member thereof, is changed dueto the atmosphere in the housing. It was found that making of theatmosphere in the housing to be substantially a vacuum will enable asurface acoustic wave resonator unit exhibiting a large Q-value to beobtained.

When the surface acoustic wave resonator is sealed in the housing,inclined mounting such that a central axis of the housing and thesurface of a surface acoustic wave resonator intersect enables space inthe housing to be used effectively. Thus, problems, such as undesirablecontact between the housing and the surface acoustic wave resonator, canbe prevented. Therefore, the portion in which the leads are in contactwith the surface acoustic wave resonator may be inclined with respect tothe central axis of the housing.

To mount the surface acoustic wave resonator by the cantilever method,the piezoelectric member may be supported through a non-conductiveadhesive agent. As an alternative to this, the supporting may beperformed with conduction established in such a manner that leads areused to establish the connection with connection lands formed on thesurface acoustic wave resonator. The foregoing methods may be employedsimultaneously or, either of the two methods may be employed as the mainmethod and the other method may be employed as a second method.

When the leads are connected to the connection lands, it is desirable toprovide flat connection ends for the leads to maintain an area forconduction or to branch the leading end of the connection end into atleast two sections. Since the connection lands usually comprise aluminumbased electrodes, connection by means of a usual soldering method cannoteasily be established. Since a very thin oxide film is naturally formedon the surface of the electrode, stable electrical conduction cannoteasily be maintained using a usual conductive adhesive agent. Therefore,a conductive adhesive agent that contains an oxidation inhibitor mixedthereto is effective when used. To prevent influence of the oxide filmon the electrode, it is desirable to form at least one scratch on theconnection land after the conductive adhesive agent has been applied orto form a bump on the connection land.

The surface acoustic wave device easily raises a problem due to foreignmatter such as dust in the housing. By subjecting at least either of apair of electrodes forming the interdigital transducer to an anodicoxidation process to form an oxide film having at least a thickness of280 Å, the foregoing problem can be prevented. If either of the pair ofelectrodes forming the interdigital transducer is subjected to an anodicoxidation process, the resonance frequency in a wafer state can bemeasured. Furthermore, a resonance frequency of the surface acousticwave resonator can be adjusted by the anodic oxidation process.

By integrally molding a surface acoustic wave resonator unit and a leadframe electrically connected to the leads by using resin, a surfacemounting type device suitable to be mounted on the surface can beprovided. In a case where the housing is made of metal, molding of alead frame electrically connected to the housing and grounding of thehousing enable a surface mounting type surface acoustic wave devicecapable of withstanding noise to be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing the structure of a surface acousticwave resonator according to the present invention;

FIGS. 2(a) and 2(b) are graphs showing a comparison of thecharacteristics of surface acoustic wave resonator units between a casewhere a cantilever mounting method is employed and a case where anentire-surface bonding mounting method is employed;

FIGS. 3(a) and 3(b) are graphs showing aging characteristics attained ina case where a cantilever mounting method is employed;

FIGS. 4(a) and 4(b) are graphs showing the aging characteristicsattained in a case where the entire-surface bonding mounting method isemployed;

FIG. 5 is a cross sectional view showing a structure of a surfaceacoustic wave resonator unit having a surface acoustic wave resonatorthat is mounted in a cylindrical case by a cantilever method;

FIG. 6 is a cross sectional view showing the structure of the surfaceacoustic wave resonator unit when viewed in a perpendicular direction;

FIG. 7 is a cross sectional view showing a portion of a surface acousticwave resonator unit is mounted by a further mounting method embodiment;

FIG. 8 is a developed perspective view showing a surface acoustic waveresonator unit having a surface acoustic wave resonator mounted in abox-like case by the cantilever method;

FIG. 9(a) is a cross sectional view of the surface acoustic waveresonator unit shown in FIG. 8;

FIG. 9(b) is an enlarged view showing a portion in which the connectionwith the leads is established;

FIG. 10(a) shows a state where the surface acoustic wave resonator isaccommodated in a ceramic case by a cantilever method;

FIG. 10(b) is a cross sectional view showing the structure of a surfaceacoustic wave resonator unit comprising a ceramic case;

FIG. 11 is a cross sectional view showing the structure of a surfaceacoustic wave resonator unit employing another embodiment of thecantilever mounting method;

FIG. 12 is a graph showing results of a comparison between theatmosphere in the housing and the values of resonance resistance;

FIG. 13 is a graph showing the relationship between the Q-values andresonance frequencies in a case where the inside portion of the housingis an atmospheric state and in a case subjected to a vacuum state;

FIG. 14 is an enlarged cross sectional view showing the portion in whichthe connection land and the lead are connected to each other;

FIG. 15 is a cross sectional view showing the lead is connected byforming a bump on the connection land;

FIG. 16 is a plan view showing a state where a lead, the leading end ofwhich is branched into two sections, is connected to a connection land;

FIG. 17 is a cross sectional view showing the lead is connected byforming a stud bump on the connection land;

FIG. 18 is a plane view showing the lead is connected by providing ascratch on a connection land;

FIG. 19 is a cross sectional view showing the lead is connected to theconnection land shown in FIG. 18;

FIG. 20 is a diagram showing a pattern for oxidizing only either sideelectrode formed on a wafer for performing anodic oxidation;

FIG. 21 is a diagram showing a tool for performing the anodic oxidation;

FIG. 22 is a diagram showing a pattern for oxidizing electrodes on twosides;

FIG. 23 is a graph showing change in the thickness of the oxide filmwith respect to anodic oxidizing voltage;

FIG. 24 is a graph showing a state where the resonance frequency ischanged due to the anodic oxidizing voltage;

FIG. 25 is a perspective view showing a device of a surface mountingtype formed by molding the surface acoustic wave resonator unit shown inFIG. 5;

FIG. 26 is a diagram showing a surface mounting type device of a typehaving a surface acoustic wave resonator unit that can be grounded;

FIG. 27 is a cross sectional view showing a structure of a conventionalsurface acoustic wave resonator unit;

FIG. 28 is a diagram showing a structure of a conventional surfaceacoustic wave resonator unit different from that shown in FIG. 27; and

FIG. 29 is a plan view showing a structure of a conventional surfaceacoustic wave resonator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a surface acoustic wave resonator according to the presentinvention. The surface acoustic wave resonator 1 is formed into a base(a chip) 2 formed by cutting a piezoelectric member made of quartzcrystal, lithium tantalate or lithium niobate into a rectangular shape.The piezoelectric chip 2 according to this embodiment is, by cutting,formed into a flat rectangular shape that has, in the central portion ofa surface (a main surface) 3 thereof, an IDT 5 consisting of a pair ofelectrodes 4a and 4b. Furthermore, reflectors 6a and 6b in the form of alattice are formed on the two sides of the IDT 5 in the lengthwisedirection of the same. The pair of electrodes 4a and 4b forming the IDT5 are allowed to pass through the outside of the reflector 6a, that is,the edge of the chip 2, so as to be introduced into an end 2a of thechip 2 so that connection lands 7a and 7b each having a relatively largearea are formed. The electrodes 4, the reflectors 6 and the connectionlands 7 are usually made of an electrically conductive material, such asgold, aluminum, or aluminum-copper alloy. In view of manufacturingeasiness and cost reduction, aluminum based material has been mostwidely employed.

Mounting a Surface Acoustic Wave Resonator

FIG. 2(a) shows change in the resonance frequency (Fr) and the quantityof deformation of the chip 2 attained when the end 2a of the chip 2 of a145 MHz Rayleigh wave type surface acoustic wave resonator 1 (having alength of 6.5 mm, a width of 1.6 mm and a thickness of 0.4 mm) formed byusing ST cut quartz crystal was supported. Furthermore, FIG. 2(b) showschange in the resonance frequency (Fr) and the quantity of deformationof the chip 2 attained when an entire reverse surface 9 opposing themain surface 3 of the chip 2 was supported by using a known adhesiveagent. The quantity of deformation of the chip 2 is, as shown in FIG.2(b), indicated by a maximum quantity of deformation of the main surface3 in order to reflect distortion and warp of the chip 2.

As can be understood from FIG. 2, in a case where only the end 2a of thechip 2 is supported, that is, in a so-called cantilever mounting methodis employed, the frequency is not substantially changed, and also thequantity of deformation of the chip is very small. On the contrary, inthe case where the reverse surface 9 of the chip is bonded, that is, inthe case of a so-called entire-surface bonding mounting method, thechange in the frequency is 100 ppm or larger and also the quantity ofdeformation of the chip is 500 nm or larger, each of which isexcessively large. Since the surface acoustic wave device obtains itsresonance frequency from the surface acoustic wave on the main surface,it has been supported by a method such that the reverse surface isstrongly connected and influence on the main surface is expected to beeliminated. However, the foregoing has confirmed that the mountingmethod considerably affects the state of the chip and the resonancefrequency. The entire-surface bonding mounting method, which has beenexpected to be able to stably secure the conventional chip and obtainstable frequency, causes the quantity of the deformation of the chip tobe enlarged excessively and the resonance frequency to be changedexcessively. On the contrary, where the chip is mounted by thecantilever method the change in the frequency and the quantity ofdeformation of the chip are reduced considerably. Therefore, to obtainstable and excellent performance, it is preferable that a surfaceacoustic wave resonator be mounted by the cantilever method.

FIGS. 3(a) and 3(b) and 4(a) and 4(b) show aging characteristics wherethe foregoing surface acoustic wave resonator is mounted by thecantilever method and where the same is mounted by an entire-surfacebonding method. The foregoing figures show results of a measured ΔFr ofthe resonance frequency and ΔRr of the resonance resistance attained ina state where surface acoustic wave resonators were mounted by theforegoing respective methods, allowed to stand at 85° C. and apredetermined time has passed. The surface acoustic wave resonatormounted by the cantilever method encounters ΔFr of the resonancefrequency by about 10 ppm or smaller after 1000 hours have passed. Onthe other hand, the surface acoustic wave resonator mounted by theentire-surface bonding method has a tendency of resulting in a change ofabout 30 ppm. Also, results of the measured ΔRr of the resonanceresistance gather in the vicinity of about 0 Ω in the case of thecantilever mounting method; on the other hand the entire-surface bondingmounting method results in a tendency of having an increase in theresonance resistance Rr of about 1 Ω to 3 Ω. The foregoing agingtendency is due to hardening of the adhesive agent taking place when theentire-surface bonding mounting process is performed and due to adifference in the coefficients of thermal expansion from the mountedmember. The foregoing influences can be eliminated by employing acantilever mounting method.

The surface acoustic wave resonator mounted by the cantilever method hasexcellent aging characteristics that are superior to those attainablefrom conventional entire-surface bonding mounting methods. That is, bymounting a surface acoustic wave resonator by the cantilever method, aresonator having long term stable characteristics can be obtained, andan increase in the resonance resistance Rr can be prevented. Thus, asurface acoustic wave resonator unit having a large Q-value suitable toa stable oscillator can be obtained.

The surface acoustic wave resonator 1 can be mounted by any of thefollowing cantilever methods. FIG. 5 shows a schematic structure of asurface acoustic wave resonator unit having a surface acoustic waveresonator 1 mounted by the cantilever method by using its leads. Thesurface acoustic wave resonator unit 20 comprises a metal case 21 formedinto a cylinder having an opening at either end thereof andaccommodating the surface acoustic wave resonator 1. The opening of themetal case 21 receives a hermetic terminal 22 so that the surfaceacoustic wave resonator 1 is sealed up in the case 21. The hermeticterminal 22 has a glass portion 23 that is provided with a metal ring 24disposed on the outer periphery thereof. Two leads 25 penetrate theglass portion 23. Ends 25c and 25d of the leads 25 located in the case21 are connected to corresponding connection lands 7a and 7b of thesurface acoustic wave resonator 1. Thus, the surface acoustic waveresonator 1 is mounted by the cantilever method in the case 21 by thehermetic terminal 22 (hereinafter called a "plug member" including theleads) through the foregoing leads 25.

The leads 25c and 25d are secured to the connection lands 7a and 7b by acoupling agent 26. In order to obtain an electrical conduction, thecoupling agent 26 is made of solder or other electrically conductiveadhesive agent. It is important to connect the leads 25c and 25d to theconnection lands 7a and 7b with a low resistance, as will be describedlater in detail. The case 21 and the metal ring 24 of the plug memberare applied with plug plating 27 and case plating 28 in order tomaintain airtightness in the case, the foregoing plating serving as asealing member, also as will be described later.

FIG. 6 shows the surface acoustic wave resonator unit 20 viewed from aposition on the side portion of the surface acoustic wave resonator 1.The surface acoustic wave resonator 1 is connected to the leads 25 insuch a manner that its main surface 3 is inclined with respect to acentral axis 29 of the case 21 so that the central axis 29 and thesurface acoustic wave resonator 1 intersect. By mounting the surfaceacoustic wave resonator 1 as described above, the surface acoustic waveresonator 1 can be mounted at a substantially central portion of thecase 21, even if the leads 25 are disposed at the center of the plugmember, whereby a sufficiently large gap can be maintained from thesurface acoustic wave resonator 1 and the inner surface 21a of the case21. By creating this gap as described above, contact between the case 21and the surface acoustic wave resonator 1 can be prevented when thesurface acoustic wave resonator 1 is accommodated in the case 21,whereby a factor that makes oscillation instable can be eliminated.Furthermore, a problem that the resonator comes in contact with theinner surface of the case 21 and thus dust is generated can beprevented.

It is preferable that the angle at which the surface acoustic waveresonator 1 is inclined be determined to be in a range from a position,at which the surface acoustic wave resonator 1 is in parallel to thecentral axis 29, to a degree at which the other end surface 8d of thechip 2 having no connection land intersects the central axis 29. Sincethe end 25c of the leads 25 is connected by the adhesive agent 26 andtherefore, the necessity of direct contact with the connection lands canbe eliminated, the mounting angle can easily be provided. As a matter ofcourse, the end 25c of the leads 25 may be inclined to make apredetermined angle or the end 25c of the leads 25 may be cut ordeformed to use the cut surface or the deformed surface to establish theconnection with the connection lands 7.

FIG. 7 shows an example in which a non-conductive adhesive agent 30 isused to mount the surface acoustic wave resonator 1 on the plug memberby the cantilever method. Since the leads 25c and 25d are, in theillustrated example, connected to the connection lands 7a and 7b usingthe conductive adhesive agent 26, the non-conductive adhesive agent 30is used to reinforce the portion mounted by the cantilever method. Theoscillations of the surface acoustic waves are generated on the surfaceof the chip 2, and the chip must have a thickness that enables thecharacteristics of the surface acoustic wave resonator 1 to bemaintained. The thickness is sufficient to be about 10 times thewavelength of the surface acoustic wave. If the resonance frequency islow, the chip is thickened, and therefore the weight of the surfaceacoustic wave resonator is enlarged. In the foregoing case, it ispreferable that both conductive adhesive agent 26 and the non-conductiveadhesive agent 30 be used to mount the surface acoustic wave resonator 1by the cantilever method with the strength enabling the same towithstand impact and vibrations. It is preferable that the area for thenon-conductive adhesive agent 30 to cover the surface acoustic waveresonator 1 be minimized. In consideration of the characteristics of thesurface acoustic wave resonator, it is preferable that the area coversthe connection lands 7, that is, so the adhesive agent 30 does not reachthe reflector 6a adjacent to the end 2a at which the chip is mounted bythe cantilever method.

FIGS. 8 and 9(a) and 9(b) show the surface acoustic wave resonator 1mounted into a flat-box-like case 21 formed into a substantially ovalshape. As shown in FIG. 9, two leads 25 penetrate an insulating member31a at an end of a flat base 31 having a substantially oval shape. Theleads 25 have, at leading ends thereof, flat connection ends 25cextending along the base 31. On the connection ends 25c, the connectionlands 7 of the surface acoustic wave resonator 1 are mounted. The leads25 and the connection lands 7 are secured by the conductive adhesiveagent 26. Furthermore, the end 2a of the surface acoustic wave resonator1 is secured by the non-conductive adhesive agent 30. The above securingmethod enables the surface acoustic wave resonator 1 to be mounted in athin case 21 by the cantilever method. The case 21 may, of course, beformed into a round can shape or a square box-like shape.

The surface acoustic wave resonator 1 may be attached in such a mannerthat its main surface 3, having the IDT formed thereon, faces the base31 in a manner contrary to FIGS. 9(a) and 9(b). In the foregoing case,the space from the main surface 3 and the base 31 is narrow, wherebyforeign matter cannot easily be introduced and satisfactory reliabilitycan be obtained. By employing the cantilever mounting method, the mainsurface may be caused to face either side. The positions of theconnection lands 7 may be suitably positioned, except on the mainsurface 3 having the IDT formed thereon. They may be formed on thereverse surface 9, the side surfaces 8a and 8c or the side surface 8bshown in FIG. 1. Also where the connection lands 7 are formed on thereverse surface 9 or the side surfaces 8a and 8c, it is preferable thatthe positions of the connection lands 7 be at the end 2a at which thechip is secured, in order to prevent deterioration in thecharacteristics of the surface acoustic wave resonator. It is preferablethat the connection lands 7 be disposed adjacent to the reflector 6anear the end 2a at which the chip 2 is secured, or disposed at aposition more adjacent to the end 2a at which the chip 2 is secured,than the reflector 6a. In particular, it is preferable that theconnection lands 7 be formed more adjacent to the securing end 2a thanthe reflector 6a, similar to the case where they are disposed on themain surface 3. Since a conductive pattern must be formed by using atechnique, such as the diagonal evaporation, the connection lands areformed at positions except on the main surface, attention must be paidto prevent defective conduction. To prevent defective conduction, it isimportant to maintain a sufficiently large area for fixing theconductive pattern. In view of the foregoing, it is preferable thatconnection lands be formed on the main surface.

FIG. 10(a) and 10(b) shows an example of the surface acoustic waveresonator unit 20 having the surface acoustic wave resonator 1 mountedby the cantilever method in a ceramic case 32. The ceramic case 32 isformed in a box-like shape having wall surfaces on all sides, at leastone of the wall surfaces having a stepped portion 32a. The steppedportion 32a has, on the surface thereof, a pattern 33 extending to theoutside of the ceramic case 32. By aligning the position of theconductive pattern 33 and those of the connection lands 7 of the surfaceacoustic wave resonator 1 to one another, the surface acoustic waveresonator 1 can be mounted by the cantilever method. When the surfaceacoustic wave resonator 1 is mounted, the connection lands 7 and theconductive pattern 33 are connected to one another by the conductiveadhesive agent 26 and the chip securing end 2a is secured to the steppedportion 32a by the non-conductive adhesive agent 30. After the surfaceacoustic wave resonator 1 has been mounted, a cover 34 is put on theceramic case 32 and the case is sealed by seam welding.

FIG. 11 shows another embodiment in which the surface acoustic waveresonator 1 is mounted into the ceramic case 32 by the cantilevermethod. In this example, the securing end 2a of the surface acousticwave resonator 1 floats from a bottom surface 32b of the ceramic case 32by means of a non-conductive adhesive agent or a spacer 35 made of, forexample, ceramic so as to be secured. Furthermore, a bonding wire 36establishes the electrical connection between the surface acoustic waveresonator 1 and the conductive pattern 33.

For the non-conductive adhesive agent for fixing the surface acousticwave resonator 1 when the surface acoustic wave resonator 1 is mounted,it is preferable that a thermosetting resin which has a heat resistancecapable of sufficiently maintaining the strength thereof in thetemperature range so the surface acoustic wave resonator unit can beoperated and that does not generate a gas that affects the atmosphere inthe case that accommodates the surface acoustic wave, be used.Furthermore, it is preferable that the resin not drop, to preventspreading to reach the surface acoustic wave resonator and the outersurface of the plug member during hardening. In addition, it ispreferable that the resin have a low stress, to prevent accumulation ofstress of the surface acoustic wave resonator chip during hardening andthe same be hardened at low temperatures. As a non-conductive adhesiveagent that satisfies the foregoing conditions, an epoxy adhesive agentcan be employed, which can be hardened when it is irradiated withultraviolet rays or when it is heated.

When the surface acoustic wave resonator is mounted by the cantilevermethod, its overall body, except the secured end thereof, is caused tofloat so that dynamical influences, such as pressure and distortion, andthermal influence from the base can be eliminated satisfactorily, ascompared with the case where conventional entire-surface bondingmounting method, is employed. Although influences, such as distortion,upon the secured end cannot be prevented, the portions that can bedistorted are made to be the outsides of the two reflectors interposingthe IDT that entraps the oscillation energy, so that the influence onthe oscillation portion can be eliminated. Therefore, the foregoingcantilever mounting method enables a surface acoustic wave resonatorunit that is free from machining distortion to be obtained. Thus, a highquality surface acoustic wave device that is not affected by change inthe atmosphere can be provided.

Atmosphere In The Housing Accommodating The Resonator

To mount a surface acoustic wave device without any influence of theatmosphere, the surface acoustic wave resonator is accommodated in ahollow housing, such as a cylindrical case, a flat case in the form of abox or a ceramic case. FIGS. 12 and 13 represent influences of theatmosphere in the housing upon the resonator unit.

FIG. 12 shows a resonance resistance Rr of surface acoustic waveresonator units shown in FIG. 7, which comprise an ST-cut Rayleigh waveof 145 MHz type surface acoustic wave resonator that is sealed in avacuum state in a cylindrical metal case having an opening at an endthereof, the pressure in which is 1×10⁻⁵ torr or lower; and a surfaceacoustic wave resonator unit that is sealed under the atmosphericpressure. As can be understood from FIG. 12, the resonance resistance Rrcan be reduced by about 3Ω to 5Ω by sealing the surface acoustic waveresonator unit under vacuum pressure as compared with the surfaceacoustic wave resonator unit that is sealed under atmospheric pressure.Thus, the surface acoustic wave device, which is a device using thesurface acoustic wave of a piezoelectric member, is affected by theatmosphere surrounding the device and that making the atmospheresurrounding the surface acoustic wave resonator to be a vacuumatmosphere will realize a resonator the deterioration of which can beprevented. If the value of the resonance resistance Rr can be reduced, asurface acoustic wave resonator unit having a large Q-value can beprovided.

FIG. 13 shows the Q-values of surface acoustic wave resonator units ofan ST-cut Rayleigh wave type having a resonance frequency of 100 MHz to300 MHz that are respectively sealed in the atmosphere and vacuum. TheQ-values undesirably decrease in inverse proportion to the frequency.Therefore, it is, as described above, important that a surface acousticwave resonator unit having a large Q-value in a high frequency range isobtained in order to realize a stable and high-frequency oscillator. Ascan be understood from the figure above, sealing in a vacuum willprovide a resonator having a Q-value at about 200 MHz that is larger byabout 60%, as compared with that attained from the case where sealingunder the atmosphere pressure is employed.

To seal the inside portion of the housing in a vacuum, a cylindricalcase of a type as shown in FIG. 5 can be employed preferably. The shapeshown in FIG. 5 is a press-fitting type cylindrical shape for sealingthe inside of the housing in an airtight manner. The case 21 is made ofa material, such as nickel silver, so that when the plug member ispress-fit, a tightening force, generated in the case 21, enablesairtightness to be maintained. Between the case 21 and the plug member,there is applied a case plating and plug plating using soft metal havingmalleability, such as solder or gold, solder being employed in thisembodiment, because the cost of which is low and exhibits excellent massproductivity. Therefore, the solder acts as a sealing member so that thegap between the case and the plug member can be plugged. The platingprocess is usually performed by a plating technique, such as a barrelmethod or a dipping method. At least an internal surface of the case,with which the plug member is brought into contact, is applied withplating, while the metal ring 24 and the leads of the plug member areapplied with plating. Plating exhibiting excellent sealing performanceand having malleability may be applied to at least the plug member orcase, while other plating processes may be performed by nickel or thelike.

If the foregoing press-fitting case is employed, sealing performed insuch a manner that the plug member to which the surface acoustic waveresonator is secured is mounted, will make the inside portion of thecase to be the same as the atmosphere in which the sealing operation isperformed. Therefore, if machining in an atmosphere of a vacuum isemployed, the inside portion of the case can be made to be a vacuum. Ifmachining in an atmosphere of nitrogen is performed, the inside portionof the case can be made to be a nitrogen atmosphere. Therefore, asurface acoustic wave resonator unit having a case, the inside of whichhas been made vacuum and that exhibits a large Q-value, can bemanufactured in large quantities and with a low cost by simply aligningthe position by using a jig.

By making vacuum the inside of the housing that seals the surfaceacoustic wave resonator, oxidation of the electrodes can be prevented.Furthermore, a short circuit of the IDT, which is formed in the order ofmicrons, due to dew condensation can be prevented so that the agingprevention is improved. The effects of preventing oxidation of theelectrodes and a short circuit due to dew condensation are also obtainedfrom sealing of the inside portion of the housing with an inactive gas,such as nitrogen. By sealing inactive gas in the housing and raising theinternal pressure, the generation of harmful gas from the adhesive agentor the like can be prevented.

Conduction Among Connection Lands, Leads and the like

The surface acoustic wave resonator according to this embodiment haselectrodes made of aluminum or aluminum based material. Where aluminumelectrodes are used, the surface is naturally oxidized to cause an oxidefilm to be formed, thus resulting in that soldering cannot be performed.Although soldering may be performed by using flux for aluminum, aprocess, such as washing for maintaining the quality, is required. Thus,mass productivity deteriorates and manufacturing cost is undesirablyraised. Accordingly, the connection lands 7 as shown in FIG. 14 areconnected to the leads 25 or the deducing pattern by using theconductive adhesive agent 26. It is preferable that the conductiveadhesive agent 26 be mixed with an oxidation inhibitor to preventoxidation of the electrodes. To obtain excellent electrical conduction,it is preferable that silver or copper be employed to make the filler (amaterial for realizing the conductive characteristic in the conductiveadhesive agent).

By using a conductive adhesive agent, a low resistance surface acousticwave resonator unit can be obtained with a low cost required. Since thenon-processed oxide film 37 is left on the surface of the aluminumelectrodes, a direct-current conduction cannot be established.Therefore, to reduce the resonance resistance Rr and obtain a surfaceacoustic wave resonator unit having a larger Q-value, the oxide film 37must be processed.

FIG. 15 shows a bump 40 provided at the connection land 7. Theconnection land 7 made of aluminum or aluminum-copper alloy has the bump40 formed thereon, which cannot easily be oxidized and exhibitsexcellent conductivity, for example, gold, silver, solder or the like,by a machining technique, such as sputtering, ion plating or the like.The bump 40 is not affected by the oxide film or the like. Therefore, ifthe leads 25 or the like including the bump 40, are attached on theconnection land 7 by the conductive adhesive agent 26, direct-currentconduction can be established and a surface acoustic wave resonator unithaving a low resonance resistance Rr and a large Q-value can beobtained. If a soldering plating covering the leads 25 is melted, inplace of fixing, using the conductive adhesive agent, the connectionwith the bump 40 can be established without using flux. In the foregoingcase, it is preferable that a non-conductive adhesive agent be used fora reinforcement to obtain the strength required to mount the surfaceacoustic wave resonator 1 by the cantilever method.

FIG. 16 shows the leads 25 connected to the connection lands 7 viewedfrom a position above the main surface 3. The connection end 25c of theleads 25 according to this embodiment is deformed into a flat shape andbranches into two sections. The two branched sections are attached bythe conductive adhesive agent 26 so they extend on the two sides of thebump 40. By deforming the connection end 25c of the lead, its area thatis in contact with the conductive adhesive agent 26 can be enlarged,whereby the contact resistance can be reduced. Simultaneously, a largeadhesive force can be obtained. By branching the connection end 25c intotwo or more sections, disposition while being combined with the bump 40formed on the connection lands 7 can easily be performed. Therefore,areas of the connection lands 7 can effectively be used and an excellentconduction with the bump 40 can be established. By providing theforegoing branch, the leads 25 can be strongly secured by the adhesiveagent 26 so the surface acoustic wave resonator 1 is mounted by thecantilever method using the leads 25.

FIG. 17 shows a stud bump 41 provided for the connection land 7 by thewire bonding method. The stud bump 41 can be formed by removing theoxide film 37 by ultrasonic vibration and by wire-bonding metal, such asgold or copper. Even if the oxide film 37 is relatively thick, the studbump 41 can be provided at a low cost and with simple work. In a casewhere the bump is formed by evaporation or the like, large energy isrequired if the oxide film is thick, and thus a large cost is required.Therefore, the stud bump 41 according to this embodiment exhibitsexcellent mass productivity and enables the cost required formanufacturing to be reduced. As a matter of course, a similar effect canbe obtained from the stud bump 41 even where a wire is arranged on theconnection land 7. By providing the bump for the connection land 7 asdescribed above, the contact resistance with the leads can considerablybe reduced. As a result, the resonance resistances Rr of a surfaceacoustic wave resonator unit (a cylindrical surface acoustic waveresonator unit oscillating a resonance frequency of 145 MHz) having nobump at the connection land distribute widely to about 20Ω to 40Ω,whereas provision of the bump is able to reduce the resonance resistanceto about 10Ω to 20Ω. By providing a bump, variation of the resonanceresistance Rr can be within a narrow range, whereby a surface acousticwave resonator unit exhibiting stable performance can be obtained.

FIGS. 18 and 19 show another embodiment for establishing a conductionwith the connection land 7. In this embodiment, the lead 25 is mountedon the connection land 7, followed by an application of the conductiveadhesive agent 26. The surface of the connection land 7, covered withthe adhesive agent 26, is scratched by a jig having a sharp leading endbefore the adhesive agent 26 is hardened. The scratch 42 may consist ofone or more lines to run parallel to the leads 25 or perpendicular tothe same. By forming the scratch 42, a portion from which the oxide film37 has been removed can be formed to cause the aluminum portion of theconnection land 7 to be exposed. Therefore, direct-current conductioncan be established between the connection land 7 and the leads 25through the conductive adhesive agent 26. If a scratch is formed on theoutside of the range for the adhesive agent 26, the exposed portion isinitially oxidized and an oxide film is again synthesized, thusrequiring attention to be directed there. If the connection land isseparated by the scratch 42, the conduction of the electrodes cannoteasily be established and the scratch out of the adhesive agent causesthe oxide film to be formed, thus requiring attention to be directedthere.

The scratch 42 can be formed by pressing the leads 25 against theconnection lands 7, by mechanically vibrating the same with ultrasonicvibrations or the like. If the adhesive agent 26 is applied by adispenser or the like, the scratch may be formed by the leading end of anozzle of the dispenser, when the agent 26 is applied. As an alternativemetal, except the lead, may be vibrated or rubbed to form the scratch.The thus-formed scratch is able to reduce conduction loss of theconnection land due to contamination or the like. Note that the processmust be performed before the adhesive agent 26 is hardened. The scratchis able to improve the value of the resonance resistance Rr, similarlyto the case where the bump is formed. In particular, it is preferablethat the scratch be formed in a line rather than formed as a dot.Furthermore, random formation of three or more lines of scratches willattain an effect similar or superior to that obtainable from the formedbump. In addition to the resonance resistance Rr, the inventor hasmeasured change in the direct-current resistance value. In accordancewith the results of the measurement, no process of the oxide filmresults in a wide range of the direct-current resistance from 5Ω toinfinite, whereas the scratch or the bump results in accurateconvergence to values about 1Ω to 2Ω. Thus, the formed scratch or bumpenables the influence of the oxide film to be eliminated, so that asurface acoustic wave resonator unit having a low connection resistance(direct-current resistance) and exhibiting a large Q-value is realized.

To obtain the foregoing effects, a scratch where the oxide film has beenremoved is required for the connection land. Therefore, the scratch isprovided for the connection land after the conductive adhesive agent hasbeen applied. In a contrary case where the scratched connection landsand the leads are connected to one other in a state of a low connectionresistance, the foregoing scratches are formed after an adhesive agenthas been applied. If the scratches are formed and the internal surfaceof the scratch is again oxidized, a satisfactory conductive state cannotbe obtained. Accordingly, it is preferable that a conductive adhesiveagent of a type containing an oxidation inhibitor mixed thereto beemployed. As the oxidation inhibitor, a reducing type inhibitor, such ashydroquinone, catechol, or phenol, is employed. Furthermore, mixing ofdifferent type metals, such as nickel, may be mixed, in addition tosilver particles, to stabilize the contact resistance and to attain aneffect of preventing oxide film being formed.

Also, the effect of the oxidation inhibitor has been confirmed due toexperiments performed by the inventor. A surface acoustic wave resonatorunit, in which an adhesive agent having no oxidation inhibitor was usedencountered change in the resonance frequency by 100 ppm or more due toannealing at 230° C. for 10 hours after the adhesive agent had beenhardened. Also the value of the resonance resistance Rr was resulted inrise to 30Ω to 40Ω as compared with a value of 20Ω or less beforeannealing was performed. If an adhesive agent containing an oxidationinhibitor is used, the change in resonance frequency can be convergedwithin about 20 ppm, and a satisfactory value of the resonanceresistance Rr of 20Ω or less can be maintained.

Protection of Electrodes

In the present invention, the surface acoustic wave resonator is mountedby the cantilever method in such a manner that it is supported whilebeing caused to float from the housing, such as a cylindrical or ceramiccase. Furthermore, a space is provided around the surface acoustic waveresonator to protect the surface acoustic wave resonator from beingaffected from the surrounding atmosphere. In the foregoing surfaceacoustic wave resonator unit, the space formed around the surfaceacoustic wave resonator serves as a space in which foreign matter, suchas dust of SUS or solder dust, that can be mixed when the surfaceacoustic wave resonator is sealed, can move. The foregoing foreignmatter is able to move between the electrodes of the surface acousticwave resonator, for example, the electrodes of the IDT or the electrodesthat establish the connection between the IDT and the connection land.Since the IDT is in the order of microns, existence of the conductiveforeign matter between the electrodes causes a short circuit to takeplace. Thus, the stable operation of the surface acoustic wave resonatorunit is inhibited. Furthermore, it is difficult to completely preventthe mixture of foreign matter. Since the surface acoustic wave resonatorunit is used in a variety of purposes, the foreign matters can move dueto impact during mounting or transporting or due to the angle ofmounting. Therefore, it is difficult to completely prevent the foregoingproblem at the time of assembling the surface acoustic wave resonatorunit or mounting the same.

To prevent the problem raised due to foreign matter, the IDT or the likemay be applied with a coating, such as silicon oxide. However, the layerof different material formed on the chip causes the resonance frequencyto be changed and the Q-value to be lowered. Thus, the effect of thecantilever mounting method is minimized. Accordingly, the inventor paidattention on the effect of the oxide film formed on the surfaces of thealuminum electrodes. As described above, oxide films are naturallyformed on the surfaces of the aluminum electrodes these formed oxidefilms are able to prevent short circuit. However, since the oxide filmthat is naturally formed is very thin having a thickness of 10 Å to 30Å, it cannot completely protect the electrodes from foreign matter thatmoves due to impact, such as falling.

Accordingly, in the present invention, the aluminum electrodes of thesurface acoustic wave resonator are anodic-oxidized, so that a thickoxide film having a thickness about 280 Å or thicker is formed on thesurfaces of the electrodes, in order to prevent problems taking placedue to foreign matter.

The anodic oxidation is performed by using a structure in which aplurality of surface acoustic wave patterns 51 are formed on a wafer 50of a piezoelectric member, as shown in FIG. 20. In this embodiment,either of the electrodes 4a and 4b, that form the IDT 5, is subjected tothe anodic oxidation. Therefore, the wafer 50 is provided with, inaddition to a surface acoustic wave pattern, a connection line 52 thatestablishes the connection with the electrode 4a of the surface acousticwave pattern 51 and a terminal 53 that establishes a connection with apower source for anodic oxidation.

FIG. 21 shows an outline of an apparatus for performing the anodicoxidation. A tank 55 includes anodic oxidation liquid 59 and a clip 56that holds the terminal 53 of the wafer 50 so the wafer 50 is immersedin the oxidizing liquid 59. A power source 57 is used to supply electriccurrent so that the portion including the wafer 50, is made to be ananode. Also, a cathode 58 immersed in the oxidizing liquid 59, isconnected to the power source 57. In this embodiment, anodic oxidationenables a non-porous oxide film to be formed. Therefore, the oxidizingliquid 59 is water solution of phosphate or liquid mixture of a watersolution of borate. As an alternative, a water solution of a salt nearneutral, such as citric acid or adipic acid, may be used. It ispreferable that the temperature of the liquid be near room temperaturein order to prevent porous film being formed. For example, in a casewhere water solution of borate is used, it is preferable that thetemperature be about 20° C. to about 30° C.

If anodic oxidation is performed under the foregoing conditions, oxidefilms each having a thickness that is substantially in proportion to theapplied voltage can be formed on the surfaces of the electrodes. Tocontrol the thickness of the oxide film and to control the electriccurrent flowing when the electric current is supplied to be a levellower than a predetermined level, it is preferable that aconstant-voltage and constant electric current power source be employedas the processing power source. Since it is preferable that portions ofthe electrodes corresponding to the connection lands be subjected to aprocess for removing the oxide film as described above, it is preferablethat the portions corresponding to the connection lands be applied witha resist or the like, to prevent an increase in the thickness of theoxide film.

The inventor has measured frequency of generation of problems in a casewhere foreign matter (SUS dust having diameters from 5 μm to 10 μm) ofSUS was forcibly mixed into a cylindrical case. As a result, about 100%of resonators that were not subjected to anodic oxidation encountered ashort circuit after a repeated falling test (results of the fallingtests repeated five times from height of 75 cm to 150 cm). On the otherhand, surface acoustic wave resonator units having the electrodes oneither side of the IDT being subjected to the anodic oxidation resultedin the frequency in the generation of short circuits being decreased.Where the anodic oxidation voltage was made to be about 30 V, thefrequency in the generation of short circuits can be substantiallyhalved. If the anodic oxidation voltage was raised to a level higherthan 50 V, the frequency in the generation of short circuits can besubstantially eliminated. Electrodes on the two sides of the IDT can beanodic-oxidized by using a pattern shown in FIG. 22 or by a similarmethod. Resonators of this type resulted in the frequency in thegeneration of short circuits being substantially eliminated when theanodic oxidation voltage was made to be 20 V or higher. As shown in FIG.23, when the anodic oxidation voltage was 20 V, the thickness of theoxide film was about 280 Å, whereas it was about 700 Å when the anodicoxidation voltage was 50 V.

Where an oxide film is forcibly formed on the electrodes on either sideof the IDT, the film must have a thickness thicker than the oxide filmsformed on the electrodes on the two sides, the required thickness beingabout two times as a result of conducted experiments. However, since theelectrodes on either side of the IDT can be individually formed for eachpattern, the resonance frequency for each pattern can be previouslymeasured in a wafer state, before chips are formed by cutting. Inaccordance with the measured resonance frequency, the process forforming the oxide film is repeated to enable the operations foradjusting the resonance frequency during the manufacturing process, suchas the major adjustment in the wafer state and the minor adjustment foreach surface acoustic wave resonator to be performed.

FIG. 24 shows changes in the resonance frequency of a plurality ofwafers with respect to the anodic oxidation voltages where the anodicoxidation voltage is about 50 V. As can be understood from the abovefigure, adjustment of the oxidation voltage enables resonance frequencyto be adjusted in units of ppm. Therefore, if the electrodes on eitherside of the IDT are anodicoxidized, the resonance frequency can bemeasured in the wafer state. In accordance with the measurements, anodicoxidation is further performed, and therefore surface acoustic waveresonators having arranged resonance frequencies can be easily obtained.Thus, the anodic oxidation of the electrodes will enable devices to berealized that exhibit durability against problems due to dust, so thatthe foregoing excellent characteristics can be maintained.

Surface Mounting Type Device

FIG. 25 is a perspective view in which the surface acoustic waveresonator unit 20 having the surface acoustic wave resonator shown inFIG. 5 accommodated in a cylindrical case by the cantilever mountingmethod so as to be formed into a surface mounting type device 60. In thedevice 60, leads 25a and 25b outwardly project over the case 21, inwhich the surface acoustic wave resonator is airtight-sealed, and areattached to corresponding lead frames 61a and 61b by, for example,welding, soldering or a conductive adhesive agent. Furthermore, a leadframe 62 is disposed on a side of the cylindrical case 21 opposing theside on which the leads project. The lead frames 61 and 62 and the case21 are integrated by a resin 65. The lead frames 61a and 61b are used toestablish electrical connection with the surface mounting type surfaceacoustic wave resonator unit 60. The lead frame 62 is used as a dummylead to maintain the strength when the surface acoustic wave resonatorunit 60 is mounted on the board. Since the elements are integrallymolded into a rectangular parallelpiped by resin 65, mounting on thesubstrate can be performed using an automatic mounting technique.

FIG. 26 shows a surface mounting type surface acoustic wave resonatorunit 60 in which the lead frame 62 is used, in the foregoing embodiment,as the dummy lead, and is electrically connected to the cylindrical case21. The lead frame 62 can be electrically connected to the case 21 at aposition 69 which comes in contact with the case 21 by a method, such ascontact, press fit, soldering or a conductive adhesive agent. Bybringing the lead frame 62 into contact with the case 21, as describedabove, the metal case 21 can be connected to the ground, that isgrounded through the lead frame 62. The surface acoustic wave resonatorunit is usually used at a high-frequency of several hundred MHz. Thus,grounding of the case 21 can shield noise existing as electric waves inspace. Furthermore, the surface acoustic wave resonator unit serving asthe noise source can be prevented. By grounding a metal case, such asthe box-like case, as well as the cylindrical case grounded through thelead frame, a surface acoustic wave device of a surface mounting typeable to withstand noise can be provided.

Each of the foregoing surface acoustic wave devices has the surfaceacoustic wave resonator mounted in the case by the cantilever method.Thus, a surface acoustic wave resonator unit capable of generating verystable resonance frequency can be obtained. Furthermore, the surfaceacoustic wave resonator unit has excellent characteristics, such as alow resonance resistance and a large Q-value. In addition,integral-molding with the lead frame by a resin enables a surfacemounting type device exhibiting excellent surface mountingcharacteristics to be easily obtained. Since the surface acoustic waveresonator is mounted by a cantilever method by using a conductiveadhesive agent or non-conductive adhesive agent, it has excellent impactresistance. If anodic-oxidized films are formed on the electrodes,problems, such as short circuit due to shock can be prevented. Thus, thepresent invention enables a surface acoustic wave resonator unitexhibiting excellent conductivity and high quality to be provided.

What is claimed is:
 1. A surface acoustic wave resonator unit,comprising:a surface acoustic wave resonator, comprising:a substantiallyrectangular piezoelectric member having a main surface, a reversesurface, a first side surface and a second side surface, and a first endsurface and a second end surface, the main surface having a centralportion, a first and a second adjacent portion adjacent to the centralportion along a longitudinal axis of the member, and a first and asecond end portion corresponding to longitudinal ends of the member,wherein the central portion and the first and second adjacent portionsare disposed between the first and second end portions, an interdigitaltransducer formed in the central portion on the main surface, and afirst reflector and a second reflector formed in the first and thesecond adjacent portions, respectively, on the main surface; asupporting member for supporting said surface acoustic wave resonator,the supporting member connected to one of the first and the second endportions of the surface acoustic wave resonator; and a hollow housingfor housing the surface acoustic wave resonator, the housing having acentral axis, wherein the main surface is inclined with respect to thecentral axis.
 2. A surface acoustic wave resonator unit according toclaim 1, wherein said surface acoustic wave resonator and saidsupporting member are connected to each other through a non-conductiveadhesive agent.
 3. A surface acoustic wave resonator unit according toclaim 1, wherein the housing extends along said surface acoustic waveresonator.
 4. A surface acoustic wave resonator unit according to claim3, wherein said housing is formed of metal and is formed in a shapeselected from at least one of the group comprising a cylinder; a roundcan; and a box, said surface acoustic wave resonator is sealed in saidhousing by said supporting member, and further comprising a plurality ofleads penetrating said supporting member and electrically connected tosaid interdigital transducer of said surface acoustic wave resonator. 5.A surface acoustic wave resonator unit according to claim 4 furthercomprising a mounting for the surface acoustic wave resonator unit, alead frame electrically connected to said lead; and a lead frameelectrically connected to said housing, wherein said surface acousticwave resonator unit and said lead frame are integrally molded by resin,and the cylindrical case is electrically connected to the dummy lead ofthe lead frame.
 6. A surface acoustic wave resonator unit according toclaim 3, wherein said surface acoustic wave resonator is sealed in saidhousing and the atmosphere in said housing is substantially a vacuum. 7.A surface acoustic wave resonator unit according to claim 3, whereinsaid surface acoustic wave resonator is sealed in said housing, and aninert gas is sealed in said housing.
 8. A surface acoustic waveresonator unit according to claim 3, wherein said housing is a ceramiccase having a substantially box-like shape that is capable of sealingsaid surface acoustic wave resonator, a portion of said ceramic caseforming said supporting member, and a deducing pattern electricallyconnected to said interdigital transducer of said surface acoustic waveresonator formed on said supporting member.
 9. A surface acoustic waveresonator unit according to claim 3, wherein said surface acoustic waveresonator is connected to said supporting portion through a lead, and anend of said lead, which is in contact with said surface acoustic waveresonator, being inclined with respect to said central axis of saidhousing.
 10. A surface acoustic wave resonator unit according to claim 3further comprising a mounting for the surface acoustic wave resonatorunit, wherein a plurality of leads electrically connected to saidinterdigital transducer outwardly extend from said housing, a lead frameelectrically connected to said leads are provided, said surface acousticwave resonator unit and said lead frame are integrally molded by resin,and the cylindrical case is electrically connected to the dummy lead ofthe lead frame.
 11. A surface acoustic wave resonator unit according toclaim 1, wherein at least two leads penetrate said supporting member andat least two connection lands being formed on said surface acoustic waveresonator as to be respectively connected to said leads; said surfaceacoustic wave resonator is attached to said supporting member throughsaid leads; and said connection lands are formed on at least one of themain surface, the reverse surface, the first and the second sidesurfaces and the first and the second end surfaces of said surfaceacoustic wave resonator in a length-wise direction of said surfaceacoustic wave resonator.
 12. A surface acoustic wave resonator unitaccording to claim 11, wherein said leads have connection ends beingsubstantially flat shapes in contact with said connection lands.
 13. Asurface acoustic wave resonator unit according to claim 12, whereinleading ends of said connection ends are branched into at least twosections.
 14. A surface acoustic wave resonator unit according to claim11, wherein said leads are connected to said connection lands by aconductive adhesive containing an oxidation inhibitor.
 15. A surfaceacoustic wave resonator unit according to claim 11, wherein said leadsare connected to said connection lands by a conductive adhesive agentand said connection lands have at least one scratch formed thereon. 16.A surface acoustic wave resonator unit according to claim 11, whereinsaid connection lands have a bump formed thereon.
 17. A surface acousticwave resonator unit according to claim 1, wherein an oxide film of about280 Å or thicker is formed by anodic oxidation on at least eithersurface of a pair of electrodes that form said intedigital transducer.18. A surface acoustic wave resonator unit according to claim 1, whereinonly either of a pair of electrodes that form said interdigitaltransducer has an oxide film of about 280 Å or thicker formed by anodicoxidation.
 19. A surface acoustic wave resonator unit, comprising:asurface acoustic wave resonator, comprising:a substantially rectangularpiezo-electric member having a main surface, a reverse surface, a firstside surface and a second side surface, and a first end surface and asecond end surface, said main surface having a central portion, a firstand a second adjacent portion adjacent to said central portion along alongitudinal axis of said member, and a first and a second end portioncorresponding to longitudinal ends of said member, wherein said centralportion and said first and second adjacent portions are disposed betweensaid first and second end portions, an interdigital transducer formed insaid central portion on said main surface, and a first reflector and asecond reflector formed in said first and said second adjacent portions,respectively, on said main surface; a supporting member for supportingsaid surface acoustic wave resonator;a housing for housing said surfaceacoustic wave resonator, said housing being formed of metal and beingformed in a shape selected from a round can or a box; and a plurality ofleads penetrating said supporting member, said leads having flat,plate-shaped end portions, said leads connected to one of said first andsaid second end portions of said surface acoustic wave resonator andelectrically connecting to said interdigital transducer of said surfaceacoustic wave resonator, wherein the lengthwise direction of said leadsis almost perpendicular to said main surface and wherein said mainsurface is attached to said flat end portions of said leads.